1. Field of the Invention
This invention relates to a control apparatus of the type in which a controlled variable from a controlled system and a target value are received as inputs and a manipulated variable of the controlled system is outputted after such processing operations as proportional integration, phase advance and phase delay are performed. More particularly, the invention relates to a control apparatus having a self-propagating function with regard to the aforementioned processing, as well as the associated control method. The invention further relates to a propagating-type controller, which is one of the elements constituting the self-propagating control apparatus, a supervisor, a method of operating the propagating-type controller, and a method of controlling the same.
2. Description of the Prior Art
The arrangement of a conventional PID-type controller is fixed to a combination of the three operations of proportion, integration and differentiation, and the parameters of each operation are adjusted by on-site technicians having special know-how. Since the arrangement of such a PID-type controller is fixed, there is a limitation upon control capability. In addition, since readjustment of the parameters requires skilled technicians, it is difficult to hold the parameters at the optimum values, which depend upon a change in the state of the controlled system at a plant or the like, a change in the working conditions, etc.
A PID-type control apparatus having an automatic adjusting function and a control system based upon modern control theory are available as techniques which compensate for the drawbacks of the PID-type controller. An optimal control system and an adaptive control system are two typical examples of control systems based on modern control theory.
A PID-type control apparatus having an automatic adjusting function refers to an apparatus which maintains excellent control capability by automatically adjusting the parameters of the PID-type controller, which performs the three operations of proportion, integration and differentiation. Rules for adjusting parameters include those derived theoretically and those derived experimentally, fuzzy-type adjustment rules and adjustment rules based on knowledge engineering. The controllers used include the conventional PID controller, I-PD controller, a PID controller having two degrees of freedom, etc.
The PID-type control apparatus having an automatic adjusting function possesses a function in which a parameter is held at an optimum value within the range of the controller incorporated in advance. With this apparatus, however, the structure of the controller is fixed at a specific combination of the three operations of proportion, integration and differentiation, and the apparatus does not possess a function for changing the controller structure itself in dependence upon the complexity of the controlled system. Accordingly, this control apparatus is incapable of demonstrating capabilities which exceed the limitations of its function as a PID-type controller.
The optimal control system, which is one of the control systems based on modern control theory, is adapted to initially obtain a dynamic characteristic of the controlled system in accurate fashion, decide the structure of the controller having the necessary complexity in accordance with the dynamic characteristic, and decide parameters based on a fixed evaluation criterion. (For example, see "Design Theory of a Linear Control System" presented by Ito, Kimura and Hosoe at the Measurement Automatic Control Society, 1978.) In accordance with the optimal control system, a capability which exceeds the limitations of the PID-type controller can be obtained from the outset. However, when a controller in which this method of control is capable of being incorporated in general form is fabricated, costs are extremely high owing to the complexity of the arrangement. In all of the examples of application so far disclosed, each control apparatus has been manufactured for a particular controlled system. Furthermore, in order to design and readjust the control apparatus, it is necessary to perform experiments for accurate identification of the dynamic characteristic of the controlled system, and the technicians concerned with adjustment must possess a high level of theoretical knowledge with regard to methods of deciding optimum gain and methods of constructing observers. In consideration of the price of the anticipated control apparatus per se, the labor required for design and readjustment and the technical level, it is clear that even if a general-purpose industrial controller based on the optimal control method is manufactured, it will merely be high in price and difficult in handling, thus making it difficult to introduce at a site which exhibits only average technical capabilities and where there is little time to spare.
Among the adaptive control systems based on modern control theory, a normative model-type adaptive control system, of which there are many practical examples, is adapted to predict the range of a fluctuation in the characteristic of a controlled system, incorporate the achievable control capability in the control apparatus in the form of a normative model in a case where the fluctuation is at its worst, and adjust the parameters in such a manner that the control system will maintain a capability the same as that of the normative model. (For example, see "Adaptive Control" by Ichikawa, Kanai, Suzuki, Kokumura, Shobido, 1984.) In regard to this system, it has been demonstrated theoretically that effective control is performed if an input richness condition and a condition relating to the fluctuation in the characteristic of the controlled system are satisfied. With such a system, a fixed control capability can be maintained which does not depend upon the fluctuation in the controlled system characteristic and the working conditions. However, as with the case of the optimal control system, a controller in which this type of control method is capable of being incorporated is high in cost. Consequently, the examples of application disclosed mainly employ a device which is separately provided. In addition, with regard to design and readjustment, a very high level of theoretical expertise is required in order to verify the input richness condition, select the normative model and verify stable conditions, etc. In the end, therefore, it is difficult to realize the controller as one which is for general-purpose, industrial use, and difficult to use the controller at a site where there is only an average technical level.
To sum up the foregoing, a PID-type control apparatus having an automatic adjusting function fixes the arrangement of the controller and adjusts only parameters and therefore is disadvantageous in that it cannot exceed the limitation upon the capabilities of the PID-type controller. On the other hand, the control systems based on modern control theory strive to perform optimal control from the start or determine the goal of the control capability in advance. Consequently, these control systems are disadvantageous in that they are merely high in cost as general-purpose controllers and require a high level of theoretical expertise for design and readjustment.